Interval Training

Interval running enables the athlete to improve the workload by
interspersing heavy bouts of fast running with recovery periods of slower
jogging. The athlete runs hard over any distance up to 1k and then has a period
of easy jogging. During the run, lactic acid is
produced and a state of oxygen debt is reached.
During the interval (recovery), the heart and lungs are still stimulated as
they try to pay back the debt by supplying oxygen to help break down the
lactates. The stresses put upon the body cause an adaptation including
capillarisation, strengthening of the heart muscles, improved oxygen uptake and
improved buffers to lactates. All this leads to improved performance.

Before undertaking interval training bear the following in mind:

Undertake a period of Continuous running before starting
Interval running

Consider the various elements of the session:

The length of the work interval, longer gives a better
effect

The pace should be comfortable raising your heart
rate to the required % of HRmax (see above)

The number of repetitions should reflect your condition and
age

The rest interval should enable you to jog and
bring the heart rate down to near 100-110 bpm

Improvements can be made by altering any of the above
variables, however you should only change one variable at a time

All changes should be gradual and take place over a
period of time

Ensure the surface to be run on is flat and even. It is usual
to do interval training on a track although it can be done on good quality
grass playing fields or on a treadmill.

GAESSER, G. A., and WILSON, L. A. (1988) Effects of continuous and interval training on the parameters of the power-endurance time relationship for high-intensity exercise. International journal of sports medicine, 9 (06), p. 417-421